I have a 99 Jeep Grand Cherokee with about 183,000 miles. Over the last couple of days it has developed a problem where when accelerating it will lose all engine power for about 5 seconds (rpms drop and and then regain power with a short burst of acceleration). It feels like it's running out of gas. I already replaced the air filter and fuel filter, those needed to be replaced anyway, but it didn't help.

Other than the power loss, it in general feels sluggish, like I'm constantly towing something. No check engine light. Any suggestions of things to check or other symptoms that I could look for that would help diagnose it?

In-line 6. I haven't noticed any oil consumption, I'm about 1000 miles into this old change and it's still at the top.
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bmbaebFeb 19 '12 at 21:29

I'm noticing a little more of a trend with the problem. It seems as though it happens within the first mile and then it generally runs better, still feels heavy but it doesn't lose power. Doesn't seem dependent on the engine being warm or cold, it's happened both ways. Today I tried releasing the gas pedal and it seemed to recover faster.
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bmbaebFeb 20 '12 at 16:46

4 Answers
4

The 4.0L is generally a very robust engine so I think the problem is with the ancillaries. Here's what I would look at:

Fuel pressure. If the car feels like you're running out of gas, it might be that the fuel pump isn't supplying enough fuel or there's another problem with the fuel system like a leaking injector. Has the fuel mileage been suffering lately?

Check the ignition components like the distributor rotor and cap if it still has a distributor, leads and spark plugs. Especially the latter if they have more than 10k miles on them, plus they're the cheapest part to change :).

As PetroEkos suggested, check for vacuum leaks

Check the emissions equipment, you might want to change the PCV valve if it hasn't been changed recently.

If it runs rough when warming up and runs a lot better when it's up to operating temperature, I would check if all the ECU temperature sensors are working as expected. If the ECU thinks that the engine is warmer than it actually is, it'll inject less fuel than it needs during warmup.

Thanks for the suggestions. Mileage has been rough, it's cold where I'm at so in winter mileage tends to drop but it seems like it's lower than it should be. I checked the spark plugs and readjusted the gap but I didn't check the rest of the ignition components, so I'll check those out. I don't remember the last time the PCV value was changed, I'll check that too and see if it's getting worn out.
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bmbaebFeb 20 '12 at 16:40

What did the spark plugs look like? Sooty? Normal? Too white, as if the engine was running lean?
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Timo GeuschFeb 20 '12 at 16:52

Some black and a little white on the ends. I'm not an expert when it comes to engines but my dad thought they looked to be of normal wear.
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bmbaebFeb 20 '12 at 17:03

1

The L-shaped electrode should be mostly white with current fuels but as long as it's not sooty I think the plugs sound OK. The whole thing also depends if you drive mostly short distances, if that's the case there's a good chance the plugs will have less white and more black on them.
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Timo GeuschFeb 20 '12 at 17:08

Thanks for the information. Sounds like it's more likely that it's something besides the plugs but I won't rule them out completely. I'll also check the ECU and see if it's malfunctioning.
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bmbaebFeb 20 '12 at 17:16